title: Osthole and imperatorin, the active constituents of Cnidium monnieri (L.) Cusson, facilitate glutamate release from rat hippocampal nerve terminals.
abstract: We examined the effects of osthole and imperatorin, two active compounds of Cnidium monnieri (L.) Cusson, on the release of glutamate from rat hippocampal synaptosomes and investigated the possible mechanism. The results showed that osthole or imperatorin significantly facilitated 4-aminopridine (4-AP)-evoked glutamate release in a concentration-dependent manner. The facilitatory action of osthole or imperatorin was blocked by the vesicular transporter inhibitor bafilomycin A1, not by the glutamate transporter inhibitor l-transpyrrolidine-2,4-dicarboxylic acid (l-trans-PDC), indicating that the release facilitation by osthole or imperatorin results from a enhancement of vesicular exocytosis and not from an increase of Ca(2+)-independent efflux via glutamate transporter. Examination of the effect of osthole and imperatorin on cytosolic [Ca(2+)] revealed that the facilitation of glutamate release could be attributed to an increase in voltage-dependent Ca(2+) influx. Consistent with this, omega-conotoxin MVIIC, a wide-spectrum blocker of the N- and P/Q-type Ca(2+) channels, significantly suppressed the osthole or imperatorin-mediated facilitation of glutamate release, but intracellular Ca(2+) release inhibitor dantrolene had no effect. Osthole or imperatorin did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization; thus, the facilitation of 4-AP-evoked Ca(2+) influx and glutamate release produced by osthole or imperatorin was not due to it decreasing synaptosomal excitability. In addition, osthole or imperatorin-mediated inhibition of 4-AP-evoked release was prevented by protein kinase C (PKC) inhibitors. Furthermore, osthole or imperatorin increased 4-AP-induced phosphorylation of PKC. Together, these results suggest that osthole or imperatorin effects a facilitation of glutamate release from nerve terminals by positively modulating N-and P/Q-type Ca(2+) channel activation through a signaling cascade involving PKC.
authors.affiliation: School of Medicine, Fu Jen Catholic University, Hsin-Chuang, Taipei Hsien 24205, Taiwan. med0003@mail.fju.edu.tw
authors.forename: Su-Jane
authors.initials: SJ
authors.lastname: Wang
authors.forename: Tzu-Yu
authors.initials: TY
authors.lastname: Lin
authors.forename: Cheng-Wei
authors.initials: CW
authors.lastname: Lu
authors.forename: Wei-Jan
authors.initials: WJ
authors.lastname: Huang
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D031048:Cnidium / Q000737:chemistry; D003374:Coumarins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D011564:Furocoumarins / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D010936:Plant Extracts / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism; D013574:Synaptosomes
chemical_list: D027322:Amino Acid Transport System X-AG; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D003374:Coumarins; D011564:Furocoumarins; D010936:Plant Extracts; D026902:Potassium Channel Blockers; D018698:Glutamic Acid; D011493:Protein Kinase C; C031534:imperatorin; C046627:osthol